Rectifier voltage shifting when standby switched on

[vmazz]

Hello helpful builders etc..Its been a long time since I asked for help..need some ..Im building an Encore Allen Amp kit(based off of a Vibrolux Reverb) for a friend. Got it up and almost running. One particular voltage that seems odd is the 5v ac tap on the rectifier goes from 5v to 13 v and sometimes 6.5v when going from standby to play. Is this telling me something? Besides this Im also troubleshooting sound from preamp, no sound yet but speaker hiss when master is cranked. Any advice is appreciated.

[Tom Phillips]

...One particular voltage that seems odd is the 5v ac tap on the rectifier goes from 5v to 13 v and sometimes 6.5v when going from standby to play...

This is interesting but I'm thinking that it's probably a measurement issue and not a fault in the circuit. Please tell us more about how you are measuring this and the test equipment you are using.

[Jazz P Bass]

Why measure the Vac of the heater?

It becomes the B+ when referenced to the center tap of the high voltage secondary.

[vmazz]

So Jazz, Are you saying when I go out of standby to play mode, the ac voltage should change? I am measuring with a Fluke MM on AC setting referenced to chassis ground. I m just trying to get voltages to see where im at. It seems to be biasing right at about 24 ma per 6v6gt with a plate voltage around 400v.

[J M Fahey]

One particular voltage that seems odd is the 5v ac tap on the rectifier goes from 5v to 13 v and sometimes 6.5v when going from standby to play. Is this telling me something?

Yes, you are measuring it wrong.
Filament voltage is measured across filament pins, period.
Not:

I am measuring with a Fluke MM on AC setting referenced to chassis ground.

[vmazz]

Thanks Juan. Sometimes I dont think clearly about what im doing, because I get ahead of myself. All the voltages now seem to be in the ballpark. No signal passing though, just hiss when master cranked. Troubleshoot will continue tomorrow if I have time. Thanks for the input, help and support!

[Jazz P Bass]

Yeah, most probably you are measuring the raw B+ ripple.

[stokes]

The 5v has no ground reference,so as Jazz says,you are measuring the ripple at the first cap.Its just like putting your meters lead at the first node in the B+ rail.

[Jazz P Bass]

I think that confuses more than a few folks

How the 5 volts is hidden in the B+, kind of.